The inventors have recently published reports that have enucleated and explained the unusual "vapochromic" changes in absorption and emission spectra that result when certain stacked platinum complexes are exposed to organic vapors; see, e.g., C. L. Exstrom et al, Chemical Materials, Vol. 7, pp. 15-17 (1995) and C. A. Daws et al, Chemical Materials, Vol. 9, pp. 363-368 (1997).
A typical experiment involves a solution, crystal or solid film of material, such as tetrakis(p-decylphenylisocyano)platinum tetracyanoplatinate (I) (see FIG. 1, which depicts the chemical formula of the compound, where the dashed vertical line indicates the c-axis) that forms stacks of alternating cations and anions with strong interplatinum interactions. These salts exhibit an intense absorption band in the visible region. Exposing the stacks to small molecule vapors, such as acetone or chloroform, leads to sorption of the vapor molecules in the free volume between the stacks, and produces shifts in the absorption and emission spectra. These "vapochromic" or "vapoluminescent" changes are usually reversible so that the original spectrum is regained quickly after the vapor is removed. Such an effect has potential application for sensor technology.
The inventors developed a new type of sensor technology, called the "vapo-chromic LED"; see, Y. Kunugi et al, Journal of the American Chemical Society, Vol. 120, pp. 589-590 (January 1998) and application Ser. No. 09/225,758, listed above.
A sandwich LED was prepared using compound 1 that gave electroluminescence from this platinum compound; see, e.g., R. H. Friend et al in Physical Properties of Polymers Handbook, J. E. Mark, Ed., AIP Press (1996); Y. Yang, MRS Bulletin, pp. 31-38 (June 1997); T. Tsutsui, MRS Bulletin, pp. 39-45 (June 1997); W. R. Salaneck et al, MRS Bulletin, pp. 46-51 (June 1997); and C. Hosokawa et al, Synth. Met., Vol. 91, pp. 3-7 (December 1997). Exposure of the device to an organic vapor sharply changed the wavelength of electroluminescence, thereby providing a new method for remote vapochromic sensing which does not require a light source.
On the other hand, photodiodes, which do require a light source, have found extensive use in the electronics industry. Organic and polymer photodiodes have been built using materials such as poly(3-alkylthiophene)s, oligothiophenes, and C.sub.60. These photodiodes give photocurrents corresponding to the absorption of light by the molecular materials. They are of interest because they can give wavelength selectivity and quantum efficiencies of more than 10% electron/photon under modest reverse bias; see, e.g., H. Yonehara et al, Applied Physics Letters, Vol. 61, pp. 575-576 (August 1992); G. Yu et al, Applied Physics Letters, Vol. 64, pp. 3422-3424 (June 1994); and Y. Kunugi et al, Chemical Materials, Vol. 9, pp. 1061-1062 (May 1997).
However, to the best of the present inventors' knowledge, a photodiode which can detect the arrival of organic vapors has not been described. Such a device would be of interest in detecting the presence of organic vapors by a change in photocurrent.